The invention relates to atomic absorption spectroscopy and more particularly to a device and technique for lighting the flame on a burner head in an atomic absorption spectrometer with an incandescent filament.
In atomic absorption spectroscopy, a measuring light beam is generated having a line spectrum identical with the resonant lines of a looked-for element. The measuring light beam is passed through a "cloud of atoms" containing the atoms of the sample to be examined in an atomic state. The atoms of the looked-for element absorb the measuring light beam since their resonant lines are identical with the line spectrum of the measuring light beam while the atoms of other elements do not affect the measuring light beam. Therefore, the absorption of the measuring light beam in the cloud of atoms provides a measure of the quantity of the looked-for elements in the cloud of atoms. The concentration of a looked-for element in a sample can be determined by this method with high sensitivity by reproducible atomization of selected sample quantities and calibration with a known calibration solution.
A flame is used in many cases for atomizing a sample. The sample is burned on a burner with an oblong burner head extending in the direction of the measuring light beam and disposed below the beam. A very hot flame, such as an air-acetylene flame, is generally necessary for atomizing a sample.
A glow filament is used in known devices for lighting the flame in the burner of an atomic absorption spectrometer. The glow filament is attached to an arm and is rotated over the burner. The arm is manually movable. This arm has to accommodate the current supply and therefore has relatively large dimensions. The glow filament is exposed to the hot flame for a short time when the flame is lit and, therefore, the useful life of the glow filament is highly limited.
For lighting a burner, it is also known to use a "pilot-flame" which is a little acetylene jet flame lit by a glow filament. The jet flame then lights the burner. This method is very expensive and requires an additional solenoid valve, an additional gas conduit and a nozzle. Because of the narrow nozzle for the pilot flame, such an arrangement is very sensitive to clogging. Furthermore, the jet flame must neither be too short nor too long so that adjustment is also necessary. The flow at the outlet of the nozzle has to be purposefully disturbed such that acetylene comes into contact with the glow filament.
It is also known to light the burner by a spark generated by means of high-voltage. Such a spark generates strong high frequency disturbances which can be reduced at high costs. In addition, a problem of protection against accidental contact is present with this method of lighting a burner.
It is an object of the present invention to provide an improved apparatus and technique for lighting a flame in a burner of an atomic absorption spectrometer.
Another object of the invention is to provide an apparatus and technique for lighting a burner which avoids overheating of the glow filament by the burner flame.
Another object of the invention is to provide such an apparatus which is economical to manufacture and durable in use.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
Accordingly, it has been found that the foregoing and related objects and advantages are attained in an atomizer burner assembly of an atomic absorption spectrometer having a burner head for emitting gas to generate an atomizer flame and a glow filament for igniting the gas positioned remote from the burner head. A gas conductor-ignition assembly conducts a portion of the gas emitted from the burner head to the glow filament for ignition to thereby light the burner head to form the atomizer flame. The gas conductor-ignition. assembly comprises a gas conducting body with an inlet end adjacent the burner head and an outlet end adjacent the glow filament so that a portion of the gas from the burner head will pass from the inlet end to the outlet end and thus to the glow filament. This gas is ignited by the glow filament and flashes back to the inlet end and thus to the burner head to light the burner head to form an atomizer flame.
The glow filament itself however is not exposed to the temperature of the hot atomizer flame. After the lighting, the gas conducting body is rotated out the area of the burner where it can not affect the further operation of the burner and no more gas is passed to the glow filament. The gas for conducting the flame from the glow filament to the burner is taken from the gas stream emerging from the burner head. Therefore, no additional means are required for generating a pilot flame.
The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.